Leakage reducing arrangement for an axial piston machine

ABSTRACT

An arrangement for reducing in a hydraulic axial piston machine, leakage from the area between the rotary cylinder block end face, and the control face of a valve plate having inlet and outlet ports. The cylinder block is mounted on the drive shaft for small axial movement, but is connected for rotation with the drive shaft by a pair of meshing gears having slanted teeth so that the end face of the cylinder block is pressed against the control face with an axial force which depends on the torque transmitted between the drive shaft and the cylinder block so that leakage from the area between the end face and the control face is prevented, irrespective of the fluid pressure and load.

[11] 3,777,623 1 Dec. 11, 1973 LEAKAGE REDUCING ARRANGEMENT FOR AN AXIALPISTON MACHINE [75] Inventor:

[73] Assignee: Robert Bosch GmbH, Stuttgart,

Germany [22] Filed: Mar. 7, 1972 [21] Appl. No.: 232,478

Paul Bosch, Ludwigsburg, Germany FOREIGN PATENTS OR APPLICATIONS1,912,243 9/1970 Germany 91/499 Primary Examiner-William L. FreehAttorneyMichael S. Striker [57] ABSTRACT An arrangement for reducing ina hydraulic axial piston machine, leakage from the area between therotary cylinder block end face, and the control face of a valve platehaving inlet and outlet ports. The cylinder block is mounted on thedrive shaft for small axial movement, but. is connected for rotationwith the drive shaft by a pair of meshing gears having slanted teeth sothat the end face of the cylinder block is pressed against the controlface with an axial force which depends on the torque transmitted betweenthe drive shaft and the cylinder block so that leakage from the areabetween the end face and the control face is prevented, irrespective ofthe fluid pressure and load.

10 Claims, 1 Drawing Figure PATENTEDBEEI 1 19H 3; 717, 623

BACKGROUND OF THE INVENTION The present invention is concerned with animprovement of axial piston machines, which may be pumps or hydraulicmotors of the type provided with a rotary cylinder block whichcooperates with a control surface of a valve plate, and has means forobtaining a sealed contact between the rotary cylinder block end face,and the stationary control face of the valve plate.

The US. Pat. No. 907,737 discloses a swash plate axial piston machinewhose cylinder block is fixedly secured to the drive shaft. Pistons inthe cylinders cooperate with the swash plate, and in order to obtain anaxial pressure between the rotary end face of the cylinder block and thecontrol face of the valve plate, three adjusting screws, spaced anglesof 120, are provided.

It is a disadvantage of this apparatus that the axial pressure betweenthe rotary end face of the cylinder block and the control face of thevalve plate must be adjusted in accordance with the maximum load, andis.

SUMMARY. OF THE INVENTION It is one object of the invention to provide ahydraulic axial piston machine in which the axial pressure of thecylinder block against a stationary valve control surface depends on theactual load to which the machine is subjected.

Another object of the invention is to reduce leakage from the areabetween the engaging rotary end face of the cylinder block and thestationary control face of the housing.

Another object of the invention is to provide a fluid film between therotary end face of the cylinder block, and the stationary control facewhich is sufficient to prevent extreme friction, but is too small tocause leakage.

With these objects in view, the present invention provides between thecylinder block and the drive shaft, a coupling means which transmitstorque between the drive shaft and the cylinder block, but has at leastone guide face slanted to the axis of the drive shaft, and exerting onthe cylinder block an axial force depending on the torque acting on thedrive shaft, and pressing the rotary end face of the cylinder blockagainst the stationary control face, which is preferably provided on avalve plate abutting a housing portion.

Since the axial component of the force transmitted by the slanted guideface to the cylinder block depends on the torque transmitted from thedrive shaft to the cylinder block, a load dependent sealing contactbetween the rotary and stationary faces is obtained.

In the preferred embodiment of the invention, the' coupling includes twomeshing gears having teeth slanted to the axis of the drive shaft. Bysuitably selecting the angle at which the teeth and flank surfaces ofthe coupling gears are slanted, the axial component of the forcetransmitted by the interconnected gears, is just right to maintain asealing contact between the rotary and stationary control faces, and itis advantageous that such axial force is produced by the machine onlyduring rotation.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of the drawing is anaxial sectional view of an axial piston machine provided with anarrangement according to one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The pot-shaped housing part 1of the axial piston pump is closed by a cover 3 which has, inlet andoutlet means 19 and 20, opening in ports 19a and 20a on the innersurface 3a of cover 3. A blind bore forming a slide bearing 5 isprovided at the center of cover 3, and supports one end portion of ashaft 6 whose other end portion is mounted in a ball bearing 4 supportedby the bottom wall of the housing 1. A shaft portion projects out ofbottom wall 1, and is driven by a motor when the machine operates as apump. Shaft 6 is provided with an annular gear portion 8 having teethslanted to the direction of the axis of shaft 6.

In the interior 2 of housing 1,3 a cylinder block 9 is located, and maybe mounted on drive shaft 6 which passes through a central bore 10. Aspring ring 25 abuts a shoulder formed by the gear ring 8 on drive shaft6 at one end of a spring 26, which abuts at the other end on a springring 27 secured to the wall of the inner bore 10 of the cylinder block9. The spring 26 urges the cylinder block 9 to move in axial directionuntil its rotary end face 14 abuts the stationary control surface 15 ofa valve plate 16 which abuts the inner surface 3a of cover wall3..Cylinder body 9 has at the end of the central bore 10, an inner gearwhich has inner teeth slanted at the same angle as the teeth of theouter gear 8, and engaging the same. In substantially the same plane inwhich the gears 8 and 11 are located, an annular guide face 1a guidesthe outer cylindrical surface of cylinder block 9 and supports cylinderblock 9 for axial movement.

The valve plate 16 is provided with two partcylindrical control ports 17and 18 which communicate with the inlet and outlet ports 19a, 20a.Axially extending cylinders 12 are provided in the cylinder block 9, andare open at one end of the cylinder block so that pistons 13 located inthe cylinders 12, project out of the cylinder block. Each piston 13 hasa spherical head 22 mounted in a corresponding spherical recess of slideshoes 22a which slide along a circular path on a surface 24a of astationary swash plate 24.

The passages 21 have ports on the rotor end face 14 located along acircle corresponding to the center circle of the part-circular ports 17and 18 in the valve plate 16. Consequently, fluid flowing through inletand outlet means 19, 20, inlet and outlet ports 19a, 20a, andpart-circular ports 17 and 18, flows alternatingly into alternatepassages 21 to the cylinders 12 whose chambers are expanded andcontracted by the axial movement of the pistons 13 which depends on theslant of the swash plate 24, shown in the drawing turned an angle of 90.

When shaft 6 is not driven, spring 26 urges the cylinder block 9 to theleft as viewed in the drawing, to a position in which the rotor end face14 abuts the control surface 15. The pressure produced by spring 26 islow, since there is no fluid pressue when the machine does not operate.

When shaft 6 is driven by a motor, not shown, a torque is transmitted bythe slanted teeth of gear ring 8 to the corresponding teeth of the innergear 1 1 so that cylinder block 9 rotates with pistons 13 which areforced by the swash plate 24 to reciprocate so that fluid is suppliedthrough inlet 20 and pumped out of outlet 19.

When shaft 6 is rotated in clockwise direction as viewed from the rightin the drawing, not only torque is transmitted to the cylinder block 9,but also an axial force is transmitted from the teeth of the gear 8 tothe teeth of an inner gear 11, urging cylinder block 9 to the left asviewed in the drawing to a position in which the rotor end face 14presses against the stationary control surface 15 of the valve plate 16.The circumferential force and the axial force transmitted between theshaft 6 and cylinder block 9, together are the resultant force acting onthe teeth. Since the force exerted by the slanted teeth of gear 8 on theteeth of inner gear 11 increases with an increased load acting on thepump, and corresponding to an increased torque acting on drive shaft6,the axial component and thereby the axial pressure between the rotor endface 14 and the stationary control surface 15 is proportionallyincreased. Consequently, leakage from the area between the faces 14 and15 is prevented at all torques and loads occurring during operation, butthe pressure exerted by the rotor end face 14 on the stationary controlsurface 15 never becomes so high as to cause wear of the contactingfaces 14 and 15.

At low loads, and at low rotary speeds of shaft 6, the axial forcecomponent may be insufficient to completely seal the control faces 14and 15, and under such conditions, the axial pressure produced by spring26 is sufficient to maintain the engaging control faces 14 and 15 insliding engagement without substantial leakage.

It is evident that, if the slanted teeth coupling shown in the drawingand described above as used, the favorable effect of the axial forcecomponent is obtained only during rotation in one direction when theapparatus operates as a pump, and in the opposite direction if theapparatus operates as a hydraulic motor.

If the desired effect and axial force component is to be obtained inboth directions of rotation, the two gears have to be provided with twoaxially adjacent portions provided with teeth slanted in oppositedirection and forming an arrow pattern on the outer gear on shaft 6 andthe inner gear of cylinder block 9. The angular position of the flanksof the teeth, and the play between the teeth must be selected so thatduring rotation in ei ther direction those tooth faces abut each otherwhich produce an axial force in the desired direction for moving thecylinder block 9 toward the valve plate 16 and control surface 15.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofleakage reducing arrangement for hydraulic machines, differing from thetypes described above.

While the invention has been illustrated and described as embodied in anarrangement for reducing leakage between a rotor end face and a controlsurface of a stationary valve plate by means of an axial force producedby coupling means with slanted teeth, it is not intended to to belimited to the details shown, since various modifications and structuralchanges may be made without departing in any way from the spirit of thepresent invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledgereadily adapt it for various applications without omitting features thatfrom the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

I claim:

1. Leakage reducing arrangement for an axial piston machine, comprisinghousing means including bearing means defining an axis, and having inletmeans and outlet means, and a control surface having inlet and outletports communicating with said inlet and outlet means; rotor meansincluding a drive shaft mounted in said bearing means for rotation aboutsaid axis, a cylinder block having a plurality of cylinders open at oneend of said block, a rotor end face at the other end of said cylinderblock slidingly engaging said control surface, and passages connnectedwith said cylinders and having rotor ports on said rotor end facecommunicating during rotation successively with said inlet and outletports, means mounting said cylinder block for limited axial movement; aswash plate mounted in said housing opposite said one end of saidcylinder block; piston means in said cylinders slidingly engaging saidswash plate; and coupling means including a first part secured to saiddrive shaft and a second part secured to said cylinder block, at leastone of said first and second parts having at least one guide faceslanted to said axis and engaging the respective other part of saidfirst and second parts to transmit rotary motion from said drive shaftto said cylinder block while exerting on said cylinder block an axialforce depending on the torque acting on said drive shaft and pressingsaid rotor end face against said control surface in sealing contactwhereby leakage is reduced during torque variations.

2. Arrangement as claimed in claim 1 wherein said housing means includesa housing having said inlet and outlet means, and a valve plate abuttingsaid housing on one side thereof, and having said control surface on theother side thereof; and wherein said inlet and outlet ports arepart-circular and penetrate said valve plate so as to communicate onsaid one side with said inlet and outlet means.

3. Arrangement as claimed in claim 1 wherein said cylinder block has acentral bore through which said drive shaft passes; and furthercomprising a spring in said -central bore surrounding said drive shaftand having one end abutting said cylinder block and an other endabutting said drive shaft so that said cylinder block is biassed inaxial direction to move to a position in which said rotor end face abutssaid control face even if said axial force is small.

4. Arrangement as claimed in claim 1, wherein said mounting meansinclude a circular inner guide face portion of said housing meansslidingly engaging a peripheral circular surface portion of saidcylinder block located substantially in a plane transverse to said axisand passing through said coupling means.

5. Arrangement as claimed in claim 1, wherein said cylinder block has acentral bore through which said drive shaft passes; and wherein saidmounting means includes a portion of said drive shaft.

6. Arrangement as claimed in claim 1 wherein at least said first partincludes a set of slanted teeth disposed around said drive shaft andengaging said second part I on said cylinder block.

7. Arrangement as claimed in claim 1 wherein said cylinder block has acentral bore through which said drive shaft passes; and wherein at leastsaid second part includes a set of slanted inwardly projecting teeth insaid central bore and engaging said first part on said drive shaft.

8. Arrangement as claimed in claim 1 wherein said first part is a gearhaving teeth slanted to said axis and radially projecting from saiddrivenshaft; wherein said cylinder block has a central bore throughwhich said drive shaft passes; and wherein said second part is an innergear within said central bore engaging said gear, the engaging teeth ofsaid engaged gears having abutting tooth faces slanted the same angle tosaid axis.

9. Arrangement as claimed in claim 8 wherein each of said gears hasfirst and second gear portions whose teeth are slanted in oppositedirections relative to said axis, and wherein said first gear portionshave teeth with lateral play on one side so as to engage when said driveshaft rotates in one direction of rotation, and said second gearportions have teeth with lateral play on the pther side so as to engagewhen said drive shaft rotates in the opposite direction of rotation.

10. Arrangement as claimed in claim 9 wherein said housing meansincludes a housing having said inlet and outlet means, and a valve plateabutting said housing on one side thereof, and having said controlsurface on the other side thereof; and wherein said inlet and outletports are part-circular and penetrate said valve plate so as tocommunicate on said one side with said inlet and outlet means.

1. Leakage reducing arrangement for an axial piston machine, comprisinghousing means including bearing means defining an axis, and having inletmeans and outlet means, and a control surface having inlet and outletports communicating with said inlet and outlet means; rotor meansincluding a drive shaft mounted in said bearing means for rotation aboutsaid axis, a cylinder block having a plurality of cylinders open at oneend of said block, a rotor end face at the other end of said cylinderblock slidingly engaging said control surface, and passages connnectedwith said cylinders and having rotor ports on said rotor end facecommunicating during rotation successively with said inlet and outletports, means mounting said cylinder block for limited axial movement; aswash plate mounted in said housing opposite said one end of saidcylinder block; piston means in said cylinders slidingly engaging saidswash plate; and coupling means including a first part secured to saiddrive shaft and a second part secured to said cylinder block, at leastone of said first and second parts having at least one guide faceslanted to said axis and engaging the respective other part of saidfirst and second parts to transmit rotary motion from said drive shaftto said cylinder block while exerting on said cylinder block an axialforce depending on the torque acting on said drive shaft and pressingsaid rotor end face against said control surface in sealing contactwhereby leakage is reduced during torque variations.
 2. Arrangement asclaimed in claim 1 wherein said housing means includes a housing havingsaid inlet and outlet means, and a valve plate abutting said housing onone side thereof, and having said control surface on the other sidethereof; and wherein said inlet and outlet ports are part-circular andpenetrate said valve plate so as to communicate on said one side withsaid inlet and outlet means.
 3. Arrangement as claimed in claim 1wherein said cylinder block has a central bore through which said driveshaft passes; and further comprising a spring in said central boresurrounding said drive shaft and having one end abutting said cylinderblock and an other end abutting said drive shaft so that said cylinderblock is biassed in axial direction to move to a position in which saidrotor end face abuts said control face even if said axial force issmall.
 4. Arrangement as claimed in claim 1, wherein said mounting meansinclude a circular inner guide face portion of said housing meansslidingly engaging a peripheral circular surface portion of saidcylinder block located substantially in a plane transverse to said axisand passing through said coupling means.
 5. Arrangement as claimed inclaim 1, wherein said cylinder block has a central bore through whichsaid drive shaft passes; and wherein said mounting means includes aportion of said drive shaft.
 6. Arrangement as claimed in claim 1wherein at least said first part includes a set of slanted teethdisposed around said drive shaft and engaging said second part on saidcylinder block.
 7. Arrangement as claimed in claim 1 wherein saidcylinder block has a central bore through which said drive shaft passes;and wherein at least said second part includes a set of slanted inwardlyprojecting teeth in said central bore and engaging said first part onsaid drive shaft.
 8. Arrangement as claimed in claim 1 wherein saidfirst part is a gear having teeth slanted to said axis and radiallyprojecting from said drivenshaft; wherein said cylinder block has acentral bore through which said drive shaft passes; and wherein saidsecond part is aN inner gear within said central bore engaging saidgear, the engaging teeth of said engaged gears having abutting toothfaces slanted the same angle to said axis.
 9. Arrangement as claimed inclaim 8 wherein each of said gears has first and second gear portionswhose teeth are slanted in opposite directions relative to said axis,and wherein said first gear portions have teeth with lateral play on oneside so as to engage when said drive shaft rotates in one direction ofrotation, and said second gear portions have teeth with lateral play onthe pther side so as to engage when said drive shaft rotates in theopposite direction of rotation.
 10. Arrangement as claimed in claim 9wherein said housing means includes a housing having said inlet andoutlet means, and a valve plate abutting said housing on one sidethereof, and having said control surface on the other side thereof; andwherein said inlet and outlet ports are part-circular and penetrate saidvalve plate so as to communicate on said one side with said inlet andoutlet means.